FIG. 6 is a block diagram illustrating a conventional inverter operation command unit disclosed in Japanese Patent Disclosure Bulletin No. 1989-26393. In FIG. 6, the numeral (1) indicates a three-phase alternating-current (AC) power supply, (2) a converter circuit (rectifying circuit) for converting a three-phase AC voltage output by the three-phase power supply (1) into a direct-current (DC) voltage, (3) a smoothing capacitor, (4) an inverter circuit for converting the DC voltage into an AC voltage of a predetermined frequency by on/off switching six switching elements at determined timing (i.e., a PWM control pattern), and (5) an induction motor driven at the AC voltage of the inverter circuit (4). The inverter operation command unit is divided into an operation command device (200) and an inverter control circuit (300) connected by a connector (20). The operation command device (200) comprises keys (21), a keying-in means (22), a command data/command value judging means (23), a sending means (24), a receiving means (25), a display data output means (26), and an alphanumeric character display board (27). The inverter control circuit (300) comprises the converter circuit (2), the smoothing capacitor (3), the inverter circuit (4), a command value acceptance judging means (31), a nonvolatile memory (hereinafter referred to as the "EEROM") allowing stored data to be electrically written and erased (32), and an inverter operation means (hereinafter referred to as the "base amplifier circuit") (33). The keying-in means (22), a command data/command value judging means (23), the sending means (24), the receiving means (25) and the command value acceptance judging means (31) are functions generated by executing a predetermined operation program by means of a microprocessor (not illustrated) and are indicated as shown in FIG. 6 to simplify the description.
As indicated in an outside view, FIG. 7, the inverter operation command unit allows the operation command device (200) to be removed from and reconnected to the inverter control circuit (300). The operation command device (200) and the inverter control circuit (300) may be connected using a long cable (28).
FIG. 8 illustrates details of the button keys (21), wherein operation commands necessary to control the induction motor (5) by means of the inverter unit will be described by way of example. In this case, the inverter unit is employed to control the speed of the induction motor (5) by setting the individual operation commands indicated in FIG. 9 to optimum values in consideration of the load characteristics, such as the machine, connected to the induction motor (5) and those of induction motor (5) itself.
For example, operation command No. 1 "torque boost" indicated in FIG. 9 is used to adjust the output torque of the induction motor (5) and allows ten incremental settings e.g., 1 to 10. The operation commands No. 2 "maximum frequency" and No. 3 "minimum frequency" are used to specify upper and lower limit values of the speed of the induction motor (5), respectively, and allow speeds to be set within predetermined ranges, for example between 60 Hz=1800 rpm and 10 Hz=300 rpm (if the number of induction motor poles is four). Similarly, the other operation commands shown in FIG. 9 can be set within predetermined ranges. The operation commands indicated in FIG. 9 are only some of the commands available, which are nearly 100 in number because of the enhanced functions of the inverter unit. In order to ensure ease of setting such a large number of operation commands, the inverter unit allows command numbers corresponding to the operation commands to be entered and set from the keyboard (21a) having button keys (21).
In the keyboard (21a) shown in FIG. 8, numeral keys 0 to 9 are used to set a command number or operation command data. "." is a decimal point employed when setting the operation command data. "F1" is used to indicate that the following command number is one digit in length. "F2" is used when the command number is two digits in length. "W" is used to set data corresponding to a given command number. "R" is employed to read set data corresponding to a given command number.
Control using the button keys (21) will now be described.
For instance, the keystrokes for changing a set value, e.g., 5, of operation command number 1 "torque boost" (see FIG. 9) to a new value, e.g., 8, are as follows:
______________________________________ "F1" "1" "R" "5" is displayed on the alpha-numeric display board (27). "8" "5" changes to "8" on the alpha-numeric display board (27). "W" Data of command 1 changes to "8". ______________________________________
In the above, "F1" indicates that the command number is a one-digit number, while "1" is the command number. "R" commands a readout of the current value for the parameter, which is then changed by entry of another value, here "8". Finally, "W" commands a rewriting of the entered value "8".
In setting the data for operation command number 10 "DC dynamic braking", the setting and calling methods are the same as above with the exception that "F2" is used instead of "F1" because the command number is two digits in length:
______________________________________ "F2" "1" "R" The previously set data is displayed on the alphanumeric display board (27). ______________________________________
According to the above example, 100 operation commands, 0 to 99, can be provided. The set data is processed by the command data/command value judging means (23), the sending means (24) and the command value acceptance judging means (31), and stored in the EEROM (32). The EEROM (32) is provided with memory spaces in correspondence with the command numbers. The command data stored in the EEROM (32) is rewritten or read by decoding an instruction from the keyboard (21a) by means of the command data/command value judging means (23), the sending means (24) and the command value acceptance judging means (31).
That is, the operation commands are set as shown in FIG. 10, e.g., operation command No. 1, torque boost, is set to "5 (%)," operation command No. 2, maximum frequency, to "60 (Hz)," . . . In some cases up to 100 operation commands are set. These set operation commands are integrated into an operation command group as operation command information, which is used to operate a particular induction motor (5). FIG. 10 shows a set operation command group composed of various operation commands. Any of these commands can be called and displayed on the alphanumeric display panel (27) by entering the required data from the keyboard (21a).
Operation of the conventional inverter operation command unit is described below with reference to the flowcharts in FIGS. 11 and 12. FIG. 11 is a flowchart illustrating operation of the operation command device (200), and FIG. 12 is a flowchart showing operation of the inverter control circuit (300).
(1) Steps S1 and S2
When the power is switched on, the keying-in means (22) waits for any of the button keys (21) to be pressed. When a key on the keyboard (21a) is pressed, the keying-in means (22) judges whether the key pressed relates to command data, command value or command write.
(2) Steps S3 to S6
When the key pressed relates to command data or command value, the command data/command value judging means (23) judges the command data or the command value of that key. (steps S3 and S4) The display data output means (26) displays the command data or the command value judged by the command data/command value judging means (23) on the alphanumeric character display board (27). (step S5)
If the keys are set in advance to correspond to the operation commands as described previously, e.g., key "8" of the keyboard (21a) is for acceleration time and key "9" for deceleration time, pressing the key "8" (after pressing "F1") causes the command data/command value judging means (23) to judge that the operation command of interest is the acceleration time, thus (after pressing "R") the acceleration time is displayed. The display enables a user to confirm that the command value is correct or that a new value has been accepted so that the user may then move on to the next command data or command value. An example of command interpretation, when the previously entered command data is concerned with the acceleration time, the command data/command value judging means (23) judges the entered command value to be the length of time from a stop state to a maximum output frequency. Therefore, if a command value "5" is entered, the length of time between the stop state and the maximum output frequency is set to 5 seconds.
When the user confirms the acceptance of the command value from the display and presses the command write key, which is then confirmed by the command data/command value judging means (23), the sending means (24) transmits the operation command data and the command value, e.g., acceleration time of 5 seconds, to the inverter control circuit (300). (step S6)
(3) Steps S10 to S14
Upon receiving the command from the sending means (24) (step S10), the command value acceptance judging means (31) of the inverter control circuit (300) judges whether the induction motor (5) may be operated in accordance with the command data and command value (step S11). If operation may be performed according to the command received, the command value acceptance Judging means (31) transmits an "acceptable" message to the receiving means (25) of the operation command device (200) (step S12) and also stores the operation command data and command value in the EEROM (32) (step S13). If the operation cannot be performed according to the command received, the command value acceptance judging means (31) transmits an "unacceptable" message to the receiving means (25) (step S14).
(4) Steps S7 to S9
After the receiving means (25) has received the command data and command value "acceptable" or "unacceptable" message, the display data output means (26) judges whether the induction motor (5) can be operated (step S7), and displays on the alphanumeric character display board (2) whether the command can be executed (step S8) (step S9). When the command can be executed, the alphanumeric character display board (2) flickers the command data and the command value alternately to indicate that the command is executable. When the command cannot be executed, the alphanumeric character display board (2) flickers the command number and an error display alternately to indicate that the command is unexecutable.
(5) Step S15
When the induction motor (5) is capable of operating in accordance with the command data and the command value received, the inverter control circuit (300) controls the operation of the induction motor (5). In controlling the operation, the inverter control circuit (300) calculates acceleration, a(f.sub.0) (c/s.sup.2), at frequency, f.sub.0 (Hz:c/s), in accordance with the acceleration time, t, and operates the induction motor (5) according to those command values. For example, if the acceleration time of 5 seconds has been entered, the inverter control circuit (300) calculates the acceleration, a(f.sub.0), at the frequency f.sub.O, for the acceleration time of 5 seconds. Assuming that a maximum output frequency is f.sub.max, the acceleration, a(f.sub.0) is denoted by the following expression: ##EQU1## where, "0 Hz" indicates that the induction motor (5) is at a stop.
(6) Steps S16 and S17
The inverter control circuit (300) calculates frequency, f.sub.0 ', which should be output t seconds after the command value, f.sub.0, is output, according to the following expression (step S16): EQU f.sub.0 '=f.sub.0 +a(f.sub.0).DELTA.t
The calculated frequency, f.sub.0 ' is output as a new output frequency (step S17). Further, t' seconds after the frequency, f.sub.0 ', is output the inverter control circuit (300) calculates frequency, f.sub.0 ", according to the following expression: EQU f.sub.0 "=f.sub.0 '+a(f.sub.0 ').DELTA.t
The inverter control circuit (300) outputs the calculated frequency repeatedly and accelerates the induction motor (5) within the entered acceleration time (step S17).
By repeating the above operations, multiple operation commands can be keyed in, and the commands executed as required.
Usually, the command values of the inverter unit vary depending on the application. Even if the application is the same, the values must also be set according to the load condition. Hence, the user of the inverter unit must set each command value, requiring a change from the initial preset value, in accordance with the application and/or load conditions. Therefore, the user must alter many command data settings every time the application and/or the load conditions change.
In contrast to the above mentioned conventional unit which stores various operation commands in EEROM (32), some conventional units store the operation commands in a magnetic storage medium (e.g., a magnetic card). Japanese Utility Model Disclosure Bulletin No. 1989-6796 discloses a unit that employs a magnetic card for storing and reading values of various operation commands by means of a card reader and a read circuit installed on the inverter. FIG. 13 shows a block diagram of the aforementioned conventional unit which includes a three-phase AC power supply (11), a converter circuit (2) for converting a three-phase AC voltage output by the three-phase AC power supply (1) into a DC voltage, a smoothing capacitor (3), an inverter circuit (4), a microcomputer 6), a PWM control circuit (9), a base drive circuit (1), a reader (11) for reading set values from the magnetic card, and a setting circuit (12) for outputting various set values.
Operation of the conventional unit will now be described with reference to FIG. 11. The reader (11) reads the operation values stored on the magnetic card and outputs signals to the setting circuit (12), which then provides the signals entered by the reader (11) to the microcomputer (6). When entry of the set values from the setting circuit (12) is complete, a start signal is provided from outside the inverter, and the microcomputer (6) performs program processing in accordance with the set values and drives the PWM control circuit (9).
The operation command process of the conventional inverter operation command unit not only requires a lot of time to set commands but can also result in setting faults since the data for many operation commands must be rewritten every time the application or load conditions of the inverter unit change. Moreover, when re-setting the commands for prior application or load conditions, the previous set values must simply be recorded on paper, resulting in a complicated work process. Although one conventional unit uses a storage medium, such as a magnetic card, as a means of simultaneously changing and storing multiple operation commands set in accordance with the application and load conditions, the cost of the equipment required is significant, e.g., the reader (11) will significantly increase the price of the operation command unit.